If there is any, the redshifted resonant absorption should be at a clearly larger velocity offset (see Figure REF ) than the Keplerian speed
of the planet on its orbit around its host, which is \(v_{\mathrm {K}}= 9.4~\mathrm {km}\,\mathrm {s^{-1}}\times \sqrt{{M_{\star ,\,1}}/a_{10}}\) 
for a circular orbit, where \({M_{\star ,\,1}}\equiv {M_{\star }}/(1~{M_\odot })\)  and \(a_{10}\equiv a/(10~\mathrm {au})\) .
Thus the orbital motion will not be able to shift significantly the absorption at the central rest wavelength of H \(\alpha \) .
Similarly, the spin broadening should not be important for the line shape as a whole since young planets have equatorial spin velocities of order \(v\approx 10~\mathrm {km}\,\mathrm {s^{-1}}\)  [1]}, [2]}, [3]}, [4]}, which is much narrower than the line. However, the fine spectral features seen for the warm-population radii in the Polar or the MagAcc case (Figures REF  and REF b, respectively) would possibly be more challenging to distinguish.
On the other hand, this depends on the latitude from which the line is emitted.
